1. Field of the Invention
The present invention relates to a non-linear control type switching power supply device and an electronic apparatus (for example, a television set) using the same.
2. Description of Related Art
FIG. 18 shows a circuit block diagram and an operational waveform diagram illustrating a conventional example of a switching power supply device adopting non-linear control (herein, fixed on-time with bottom detection control). A switching power supply device shown in FIG. 18 is a synchronous rectification type voltage step-down DC/DC converter that generates an output voltage OUT of a desired level by stepping down an input voltage IN.
Examples of prior art related to the above include techniques described in JP-A-2008-29159, JP-A-2009-148155, JP-A-2009-148157, the publication of U.S. Pat. No. 7,714,547, and JP-A-2010-226930, respectively.
A non-linear control type switching power supply device is characterized in that, compared with a switching power supply device using linear control (such as, for example, voltage mode control or current mode control), a high load response characteristic can be obtained by using a simple circuit configuration.
In the non-linear control type switching power supply device, however, a switching frequency of an output transistor varies largely with an input voltage IN, an output voltage OUT, and an output current IOUT. Because of this, the non-linear control type switching power supply device has been problematic in that, compared with the linear control type switching power supply device, it is poor in output voltage accuracy and in load regulation characteristic (stability of the output voltage OUT with respect to a variation in load).
Furthermore, in a case where an attempt is made to use the non-linear control type switching power supply device as a power supply for an application involving a large input voltage variation or for an application requiring various output voltages, in order to allow power in a wide frequency band to be handled, measures should be taken to prevent EMI (electromagnetic interference) and noise, which has made set designing difficult.